1. Field of the Invention
The present invention relates to techniques for performing authentication using SIP (Session Initiation Protocol) messages. More particularly, the present invention relates to techniques for performing UMTS (Universal Mobile Telecommunications System) authentication using SIP messages.
2. Description of the Related Art
The SIP has been selected as the protocol over the UNI (User to Network Interface), that is, the interface between the mobile subscriber and the CSCF (Call State Control Function), for R00 (release 2000) and the current UMTS AKA (Authentication and Key Agreement) is one proposal for the authentication mechanism for the R00 UMTS.
The SIP has been defined in the IETF (Internet Engineering Task Force) draft standard RFC2543 (Request For Comments), issued March 1999 and the UMTS AKA has been defined in the 3GPP (3d Generation Partnership Project) specification TS 33.102, version 3.5.0, Release 1999, issued July 2000. The contents of this draft standard in its entirety and the contents of this specification in its entirety are both incorporated by reference herein.
As stated in the draft standard:                The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol for creating, modifying and terminating sessions with one or more participants. The sessions include Internet multimedia conferences, Internet telephone calls and multimedia distribution. Members in a session can communicate via multicast or via a mesh of unicast relations, or a combination of these.        SIP invitations used to create sessions carry session descriptions which allow participants to agree on a set of compatible media types. SIP supports user mobility by proxying and redirecting requests to the user's current location. Users can register that current location. SIP is not tied to any particular conference control protocol. SIP is not designed to be independent of the lower-layer transport protocol and can be extended with additional capabilities.        
However, the use of the UMTS AKA procedure to perform authentication through SIP messages has not been disclosed in the draft standard.
Furthermore, in the IP Multimedia (IM) subsystem, which supports mobile IP telephony, a subscriber authentication mechanism must be standardized. Such an authentication mechanism has not yet been standardized. However, the UMTS AKA procedure will most likely be the chosen authentication mechanism. Therefore, a technique to perform UMTS AKA using the SIP protocol must be defined.